1. Field of the Invention
This invention relates to a method for direct synthesis, by living cationic polymerization, of nitrogen-containing polymers, and particularly to the production of nitrogen-containing polymeric materials in a single step Friedel-Crafts polymerization of olefinic materials containing substantial amounts of isobutylene.
2. Description of Related Art
A review of carbocationic macromolecular engineering is provided in Kennedy and Ivan, Designed Polymers by Carbocationic Molecular Engineering: Theory and Practice, Hanser Publishers, Munich, Vienna, New York and Barcelona, Section II.3.4 which relates to mechanistic considerations: a comprehensive view of living carbocationic polymerization and the spectrum of ionicities of active species. At page 32, living polymerizations are defined as ideal living polymerization in which charge transfer and termination are absent, and quasi-living polymerizations are defined as having rapidly reversible charge transfer and/or termination present wherein the rate of these processes is faster than that of propagation. In either case the living behavior of the polymer results in a polymer in which charge transfer and termination are absent. For the purpose of the present invention, living polymers are therefore defined as polymers which have substantially and preferably no apparent chain transfer and termination. Resulting polymers have low polydispersity indices also known as molecular weight distributions of preferably less than 1.5 and in the range of 1.5 to the ideal value of 1, one (1) being where all of the molecular chains are of the same length. Cationic living polymerization systems are disclosed to take place by the polymerization reaction of monomers in the presence of a cationic initiator. A living polymerization system is one wherein the molar ratio of the monomer to initiator is equal to the degree of polymerization. The calculated molecular weight, therefore, equals the degree of polymerization times the molecular weight of the monomer plus the molecular weight of the initiator. In a living system the measured number average molecular weight should be ideally equal to the calculated molecular weight, again evidencing the absence of true termination of the polymerization system. Further detail is described in the Kennedy reference, hereby incorporated by reference.
U.S. Pat. Nos. 5,066,730 and 5,122,572 are directed to living catalysts, complexes and polymers therefrom. There are disclosed living polymers derived from isobutylene using Lewis acid catalysts and initiating systems based on organic acids or esters. The preferred Lewis acid catalyst is boron trichloride.
An early description of living polymerization using isobutyl vinyl ether was disclosed in M. Miyamoto, M. Sawamoto, T. Higashimura, Macromolecules, 17, 265 (1984).
It has been disclosed that there is an improvement in a chemical process following a "living behavior", that the polydispersity index of the polymeric products is reasonably low, lower than 1.5 in many examples, while the terminal function is still a tertiary chloride. This is the case of European Patent No. 341,012 which relates to the production of uniform molecular weight polymers. This process involves a monomer, a solvent, an initiator component having an acetate, an etherate, a hydroxyl group or a halogen function of a benzylic type initiator, a Lewis acid and an electron donor component having an electron donor number of from 25 to 50.
Chain end functionalization may result from transfer reactions such as those described in U.S. Pat. No. 4,568,732 which relates to a continuous process for forming telechelic halogenated polymers wherein a cationically polymerizable monomer and an inifer (initiator-transfer agent) are contacted with a boron chloride solvent solution. Disclosed monomers are olefins of from 4 to 12 carbon atoms, e.g. isobutylene. Suitable inifers are halogenated aromatic or aliphatic hydrocarbons, vinyl halides, silane-substituted hydrocarbyl halides, dicyclopentadienyl halides, alpha-chlorostyrene homopolymers, and 2-chloro-propene homopolymers and copolymers, wherein the halide is F, Cl or Sr. In this patent, the polydispersity index of the polymer was not particularly low, and the terminal function was a tertiary chloride which necessitates subsequent chemical steps in order to obtain the desired nitrogen-containing function.
Polymers, particularly polyolefin substrates, having nitrogen-containing functional groups such as the azide, cyano, carbonylamino or thiocarbonylamino groups are useful since the functional group is polar, and imparts desirable properties to a polyolefinic substrate. Also, these groups may act as a reactive site for further modification of the polymer. Nitrogen-containing polyisobutylenes have applications such as lube additives, compatibilizers, emulsifiers, and the like. For example, azide terminal polymers may be further modified by phthalamidation or reduction of the azide group and thus result in polymer products with useful modifications. For instance, reduction of the azide group of polyisobutylenes and addition of a polar moiety to the alpha nitrogen atom may result in improved polymeric compatibilizers, emulsifiers, etc.
Prior art processes for synthesis of polymers having nitrogen-containing functional groups, such as nitrogen-containing polyisobutylene, involve several reaction steps. Chain end functionalization is known in the field of cationic polymerization.
The art further discloses that it could be possible to achieve direct functionalization by cationic polymerization of polymers end-capped by nitrogen containing functions using, for instance, an initiator having a pseudohalogen function of the benzylic type. Pseudohalogen or halogenoids include inorganic anions, e.g., CN.sup.-, CNO.sup.-, CNS.sup.- and N.sub.3 which have properties resembling those of halide ions as disclosed in Discher, Modern Inorganic Pharmaceutical Chemistry, John Wiley & Sons, Inc., N.Y., p. 343 (1964). In a single chemical process a polymer is derived from the monomer, using an initiator having nitrogen-containing function such as azide, cyano, carbonylamino or thiocarbonylamino group. These types of results are referred to in U.S. Pat. No. 5,032,653. However, the polymeric products were not disclosed to have a narrow molecular distribution (i.e., monodispersed type). The molecular weight was controlled by the monomer feed rate and the amount of Lewis acid catalyst as well as the monomer to initiator ratio. The amount of initiator was based on a Lewis acid to initiator mole ratio of 3:1 to 1:3 with enhanced results as the ratio approaches 1:1. The molecular weight distribution (MWD) are controlled based on monomer feed rate and product removal rate.
There are three different desirable goals for the synthesis of polymers by cationic polymerization. The first is specific functionalization of the chain ends by a nitrogen-containing function, using direct synthesis from the monomer and the initiator which is incorporated in the resulting polymer. The second is easy control of the molecular weight by adjustment of the monomer to initiator ratios and low polydispersity index, (low MWD). Thirdly, it is a goal to control molecular weight and MWD in the absence of additive directed to molecular weight control.
The above references do not disclose the possibility of obtaining more than two of the above goals. For instance, U.S. Pat. No. 4,568,732 does not offer any of the three above advantages, European Patent No. 341,012 discloses a solution of only the second goal, while U.S. Pat. No. 5,032,653 combines only goals Nos. 1 and 3.
Other references of interest include U.S. Pat. No. 4,611,037 which relates to a process for preparing polymers having reactive halogen end groups employing cationically polymerizable monomers and a catalyst system consisting of a metal halide and an organic halide, wherein the metal halide is used in from 2 to 500 times molar excess, based on the organic halide.
Chain end functionalization may also be accomplished by termination reactions wherein a functional group is imparted to the electrophilic site of a developing polymer. Such systems entail high manufacturing costs and expend considerable process control resources due to the need to keep the electrophilic site available.
U.S. Pat. No. 3,684,713 relates to lubricating oil and fuel compositions containing oil-soluble azo compounds prepared by reacting an oil-soluble, synthetic organic polymer having at least 20 carbon atoms with an azo compound (e.g., azo esters, azo amides such as azodiformates and azodiformamides) at temperatures of from 20.degree. C. to 200.degree. C. oil-soluble polymers are disclosed to include polybutenes, and copolymers of isobutylene/styrene and isobutylene/1-decene.
U.S. Pat. No. 4,393,199 discloses a cationic polymerization method to produce low molecular weight polymers wherein cyclic ethers (e.g., bis(azidomethyl)oxetane-3) are polymerized in the presence of a diol/cationic catalyst for molecular weight control.
U.S. Pat. No. 4,483,978 relates to energetic copolymers by copolymerization of azido monomers (e.g., bis(azidomethyl)oxetane), wherein the N.sub.3 azido group is bonded directly to a ring carbon atom, with a cyclic oxide.
U.S. Pat. Nos. 3,993,609 and 4,029,615 relate to polymeric cellular structures obtained by mixing an acid sensitive azo compound with an acidulous or acidic polymerizable medium, such as unsaturated polyesters and polymeric active resins containing one or more terminal and/or pendant functional groups that undergo free radical reaction.
U.S. Pat. Nos. 3,645,917, 4,268,450 and 4,405,762 relate to polymers having pendant alkylazide side groups prepared by reaction of a polymer with a metal azide. In U.S. Pat. No. 3,645,917, a polyether polymer is prepared from epichlorohydrin, and then reacted with a metal azide (e.g., sodium azide) at 20.degree. C. to 150.degree. C. to form azidomethyl groups pendant from the main polyether polymer backbone. Polyether and polyester polymers are disclosed in U.S. Pat. No. 4,268,450 to be reacted with sodium azide at 100.degree. C. to form energetic hydroxy-terminated azido polymers having pendant alkyl azide groups. In U.S. Pat. No. 4,405,762, 3,3-bischloromethyloxetane is polymerized to yield halomethyl polymer products having hydroxy functionality which are then reacted with metal azide to form poly(azidomethyl oxetanes), which are disclosed to be useful as energenic binders for (e.g.) explosives.
U.S. Pat. No. 4,113,804 discloses compositions comprising polybutene, EPDM and polyolefin which are cross-linked by use of chemical free-radical generators or cross-linking agents which are disclosed to include azido formates (e.g., tetramethylenebis(azido formate)), aromatic polyamides (e.g., 4,4'-diphenylmethane diazide) and sulfonazides (e.g., p,p'-oxybis-(benzene sulfonyl azide).
European Patent Application 206,756 relates to olefin polymers such as polyisobutylene, polystyrene, polyoctene and polypropylene which are polymerized in the presence of a preformed catalyst complex of an organic acid or its ester and a Lewis acid, preferably boron trichloride. It is disclosed that the polymerization is believed to occur, e.g. in use of a catalyst complex of an ester and boron trichloride, by the opening of the ester bond and monomer insertion. The organic acids are disclosed to be mono-, di- and tricarboxylic acids and acids containing chloride, formate, allylic, acrylic or methacrylic.